Waste oils have generally been disposed of by incineration, in landfill, or used in road oiling for dust control, because the cost of reclamation and rerefining has been excessive. However, because of the rising cost of hydrocarbon fuels and lubricants, coupled with the ever-increasing demand and depletion of resources, the need for an efficient, low-cost waste oil rerefining process has arisen.
Large and increasing volumes of used oil, such as crank- case oils from diesel and internal combustion engines, cutting oil, hydraulic oil, and other oils are produced each year. These waste oils may be contaminated with oxidation and degradation products, water, fine particulates, metal and carbon and oil additive products and other contaminants not found in virgin oil. Many of these contaminants are formed from the degradation of the oil when used or are contaminants from use which become added to the oil. These contaminants can render the oils unsuitable for continued use. Thus, the considerations and problems in connection with rerefining used oil are different from those associated with the refining of virgin oil, since used oil contains contaminants not present in crude oil.
In recent years some small scale rerefining processes have been put into operation in which marketable oils are recovered. However, due to the high costs involved and the resulting narrow margin of profit, such recovery processes represent a small percentage utilization of the total quantity of used oils.
The ever-increasing scarcity and consequent high costs of petroleum, particularly high quality stocks, now presents positive incentives to selectively remove undesirable contaminants from used oils and reuse the valuable high quality components contained in such oils.
Several waste oil rerefining processes are known from the prior art. For example, in U.S. Pat. No. 3,639,229, a process is described where a mixture of an aliphatic monohydric alcohol of from four to five carbon atoms and a light hydrocarbon is added to waste oil. The mixture settles into three distinct layers. The upper oily layer is recovered, treated with sulfuric acid and thereafter refined by conventional means.
In U.S. Pat. No. 3,919,076, a process is described that involves removing water from the waste oil, adding a saturated hydrocarbon solvent, settling the mixture to recover the oil/solvent mix, removing the solvent, vacuum distilling the residual oil to collect selected fractions, hydrogenating the fractions over a catalyst, stripping hydrogenated oil to remove light ends and filtering the remaining product.
U.S. Pat. No. 4,124,492 discloses a process for reclaiming useful hydrocarbon oil from contaminated waste oil in which the waste oil is dehydrated and, thereafter, the dehydrated oil is dissolved in selected amounts of isopropanol. The undissolved waste matter is separated and the residual oil/solvent fraction is distilled to recover the decontaminated oil and solvent. The recovered oil is further clarified by treatment with a bleaching clay or activated carbon at elevated temperatures.
In U.S. Pat. No. 4,021,333, a process is described for rerefining used oil that includes distilling a volatile forecut from the oil, followed by a conventional type of distillation that may occur at reduced pressure. Use of demister means is preferred to minimize carry-over of material into the distillate. The distillation is continued until the desired recovery is obtained. The impurities present in the distillate are extracted.
A need exists for a method of effectively removing or otherwise eliminating undesirable contaminants found in used oil to make the rerefined oil more suitable for use in, for example, internal combustion engines. Further, a need exists for such a method that is feasible for use on a commercial scale.